Oxygen partial pressure controller for a pressure swing adsorption system

ABSTRACT

An oxygen partial pressure controller regulates the oxygen partial pressure (PPO 2 ) of the product gas of a pressure swing adsorption oxygen enriching system by means of a bleed valve which increases gas flow through the adsorptive system thereby decreasing the PPO 2  of the product gas. The controller includes a solenoid valve which permits the bleed valve to function when the adsorption system pressure and PPO 2  is high.

BACKGROUND OF THE INVENTION

In aircraft breathing systems where oxygen enrichment may be achievedthrough on-board oxygen generation, one means of generating an oxygenrich product gas is by fractionalizing air. Air fractionalizing isusually accomplished by alternataing the flow of high pressure airthrough each of two beds of molecular sieve material such as a zeolite.This process is identified as the pressure swing adsorption technique.

The oxygen concentration of the enriched product gas of a pressure swingadsorption system decreases as the product gas flow through the systemincreases. It is therefore possible to control the oxygen partialpressure (PPO₂) within a fixed range or vary the PPO₂ in accordance withother parameters such as breathing system pressure.

SUMMARY AND OBJECTS OF THE INVENTION

According to the invention an oxygen partial pressure controller for apressure swing adsorption system is used to control the oxygen partialpressure (PPO₂) of the product gas by bleeding a portion of the productgas to the atmosphere thereby increasing the product gas flow anddecreasing the PPO₂. The bleed flow is controlled as a direct functionof the breathing system pressure and is thereby maintained between apreset maximum and zero. A PPO₂ monitor acts in conjunction with thecontroller to establish a preset minimum PPO₂ level.

It is therefore an object of this invention to provide an oxygen partialpressure controller for a pressure swing adsorption system formonitoring and estabishing a predetermined oxygen partial pressure(PPO₂) by selectively bleeding a portion of the product gas to theatmosphere thereby increasing the product gas flow and decreasing thePPO₂.

BRIEF DESCRIPTION OF THE DRAWINGS

The sole FIGURE is a schematic representation of an oxygen partialpressure controller for use with a pressure swing adsorption system.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

An oxygen partial pressure (PPO₂) controller as schematicallyrepresented in the FIGURE is used in conjunction with an airfractionalizing oxygen enrichment system. The controller regulates thePPO₂ of the product gas of the fractionalizing system. Airfractionalizing is accomplished by alternating the flow of high pressureair through each of two beds of molecular sieve material such as azeolite. This process is referred to as the pressure swing adsorptiontechnique.

In a pressure swing adsorption system the PPO₂, or oxygen concentrationof the system decreases as the product gas flow through the systemincreases and vice versa. The controller described herein bleeds acontrolled portion of the high pressure product gas to atmospherethereby reducing the PPO₂ of the product gas by increasing the gas flowthrough the system.

Referring to the FIGURE an oxygen partial pressure controller 10includes an inlet 12 which is connected to the outlet of a pressureswing adsorption system (not shown) through which the product gas ofthat system flows. The product gas is directed in a first line 14 to theinlet of a bleed valve 16 and to the controller outlet 18. Product gasexiting the outlet 18 is piped to the user which in the example of ahigh altitude aircraft can be either the pilot through a breathing maskor the cabin in which the pilot resides.

The product gas is directed in a second line 20 through a fixed orificeflow restrictor 22 to a chamber 23 on a first side of a diaphragm 24.The product gas in the second line 20 is also directed to the inlet port26 of a normally open electrical solenoid valve 28. The outlet port 30of the solenoid valve 28 communicates with the atmosphere which in thecase of a high altitude aircraft can be represented by aircraft cabinpressure or atmospheric pressure at the aircraft altitude.

The second side of the diaphram 24 is biased by a compression spring 32and pneumatically vents to the atmosphere, cabin or altitude, through acontroller exit port 34. A stem 38 is mechanically attached to the firstside of the diaphragm 24. The stem 38 contacts a valve actuating arm 42which is rotatively attached to the controller housing 44 at a pivot 46at one end. At its other end the actuating arm 42 restrains a poppet 48of the balanced bleed valve 16 which is biased by a compression spring50. The bias level of the spring 50 is adjusted by a vented screw cap 51which threadly engages the housing 44.

The normally open solenoid valve 28 is retained open by a compressionspring 52 and is closed when coils 54 are electrically excited. Theelectrical signal for actuating the solenoid valve 28 originates in acommercially available polarographic oxygen sensor 58 which generates anelectrical signal proportional to the PPO₂. This signal is compared to apreset electrical signal in a signal conditioner 60 and when the sensoroutput exceeds this preset threshold an error signal is generated,amplified, and supplied by the signal conditioner 60 to the solenoidcoils 54 closing the valve 28.

MODE OF OPERATION OF THE PREFERRED EMBODIMENT

The product gas from a pressure swing adsorption system (not shown)enters the controller 10 at the inlet 12 and is directed to the balancedbleed valve 16 and the controller outlet 18. If the bleed valve 16 isclosed, as illustrated, no product gas is bled off. When the valve 16 isopen, a portion of the product gas bleeds past the poppet 48 and exitsto the atmosphere through the exit port 56. This bleed path toatmosphere increases the differential pressure across the pressure swingadsorption system, from its high pressure air source to the atmosphericpressure at port 56, and thus increases the gas flow through the systemthereby decreasing the PPO₂ of the gas exiting the controller at theoutlet 18 and the port 56.

The bleed valve 16 actuation is controlled by the product gas which isdirected through the line 20 through the restrictive orifice 22 and tothe chamber 23. If the coil 54 of the electrical solenoid valve 28 isnot excited, the normally open valve 28 allows the control gas to flowthrough the inlet port 26, the outlet port 30, and exit port 56 to theatmosphere thereby holding the bleed valve closed by the compressionspring 32 acting through the diaphram 24, the stem 38, and the actuatingarm 42.

An electrical signal excites the coils 54 of the solenoid valve 28 whenthe polarographic oxygen sensor 58 together with the signal conditioner60 create an error signal indicating that the PP0₂ is at or above apreset level. At that point the inlet port 26 of the valve 28 is closedand the pressure in the chamber 23 increases from the atmosphericpressure at the port 56 to the system pressure at the inlet 12. If thepressure at the inlet 12 is at or above a predetermined minimum, thepressure in the chamber 23 will displace the diaphram 24 against thecompression spring 32. As the diaphram 24 is displaced, the stem 38 isdisplaced with it allowing the spring 50 to open the bleed valve 16 bydisplacing its poppet 48 as the poppet moves the actuating arm 42 aboutthe pivot 46. If the PPO₂ level drops below the preset level,deenergizing the solenoid coils 54, opening the valve 28 and venting thechamber 23 to atmosphere and/or if the breathing system pressure at theinlet 12 and chamber 23 falls below the predetermined threshold, thespring 32 will act through the diaphram 24 and stem 38 to close thevalve 16. The pressure threshold is controlled by adjusting the bias ofthe spring 50 by means of the threaded screw cap 51.

The controller described includes an electrical solenoid which respondsto an electrical signal originating in the polargraphic oxygen sensor.Oxygen sensors are commercially available which output a pneumaticpressure signal proportional to PPO₂. It is understood that thisinvention applies equally to a controller comprised of a pneumaticallyactuated solenoid valve responding to the pressure signal of a pneumaticoutput oxygen sensor.

What is claimed is:
 1. An oxygen partial pressure controller forregulating the oxygen partial pressure (PPO₂) of the product gas of apressure swing adsorption oxygen enriching system which is operating ata system pressure applied to the inlet of the controller, in which thePPO₂ of the product gas is inversely proportional to the flow of productgas through the system, said controller utilizing a conventional PPO₂monitor and signal conditioning elements, said controller comprising:ableed valve for increasing product gas flow through the controller byincreasing the bleed flow of product gas, a diaphragm enclosing achamber and responsive to chamber pressure, a line coupling said chamberto said product gas at system pressure, and an outlet venting saidchamber to atmospheric pressure, linkage means coupled to said diaphragmfor controlling the operation of said bleed valve, and a solenoid valveresponsive to said PPO₂ monitor and said signal conditioning means forcontrolling chamber pressure, wherein said solenoid valve is operable toblock said outlet thereby increasing the chamber pressure to equalsystem pressure, and wherein said solenoid valve is operable to opensaid outlet thereby decreasing the chamber pressure to equal atmosphericpressure, wherein high chamber pressure causes said bleed valve to openincreasing gas flow and lowering PPO₂, and low chamber pressure causessaid bleed valve to close decreasing gas flow and increasing PPO₂. 2.The controller of claim 1 further comprising:adjustable spring biasingmeans for said bleed valve, whereby the PPO₂ level may be controlledrelative to atmospheric pressure by varying the bias provided by thespring.